Field of the Invention
The present invention relates to an apparatus for inspecting an edge portion of a substrate, and more particularly, to an apparatus for inspecting an edge portion of a substrate able to inspect a defect or a chamfered width on an edge portion of a substrate.
Description of Related Art
A glass substrate used in flat panel displays, such as thin-film transistor liquid crystal displays (TFT-LCDs), plasma display panels (PDPs) and electroluminescent (EL) displays, is manufactured by a shaping process of shaping molten glass produced from a glass melting furnace into a flat glass plate and a cutting process of cutting the flat glass plate according to predetermined dimensions. The manufactured glass substrate is subsequently transported to a machining line, in which the glass substrate is in turn machined. In the machining line, the glass substrate is cut again according to the dimension of a flat panel display in which the glass substrate is to be used, and subsequently the four edges of the glass substrate are chamfered. The chamfering process is intended to prevent the four edge portions of the glass substrate from being easily damaged by, for example, external impacts by making the edge portions round. When the chamfering process is carried out, as shown in FIG. 1, the edge portions of the substrate generally has the upper surface, the end surface and the lower surface. Although the chamfered upper and lower surfaces of the edge portion of the substrate are required to be symmetrical to each other, the upper and lower surfaces are, in fact, asymmetrical.
After the chamfering process, an inspection process is carried out to inspect whether or not a defect, such as a crack, has occurred on the edge portion chamfered at the chamfering process and to inspect the width of the chamfered portion.
In the related art, this inspection process is carried out by an inspection apparatus disclosed in Patent Document 1.
However, the inspection apparatus disclosed in Patent Document 1 has a drawback in that this apparatus must use a plurality of optical devices in order to inspect the upper surface, the lower surface and the end surface of the edge portion, respectively.
The inspection apparatus disclosed in the Patent Document has another drawback in that it is difficult to precisely measure the width of the chamfered portion since coaxial illumination is used. This is because the upper surface and the lower surface of the edge portion are inspected on the same line and thus the surface that is being inspected is influenced by an afterimage of a chamfering reference line occurring on the opposite side.
The information disclosed in the Background of the Invention section is provided only for better understanding of the background of the invention and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.